A Wireless Fiber Photometry System Based on a High-Precision CMOS Biosensor With Embedded Continuous-Time $\Sigma \Delta$ Modulation

Abstract

Fluorescence biophotometry measurements require wide dynamic range (DR) and high-sensitivity laboratory apparatus. Indeed, it is often very challenging to accurately resolve the small fluorescence variations in presence of noise and high-background tissue autofluorescence. There is a great need for smaller detectors combining high linearity, high sensitivity, and high-energy efficiency. This paper presents a new biophotometry sensor merging two individual building blocks, namely a low-noise sensing front-end and a order continuous-time modulator (CTSDM), into a single module for enabling high-sensitivity and high energy-efficiency photo-sensing. In particular, a differential CMOS photodetector associated with a differential capacitive transimpedance amplifier-based sensing front-end is merged with an incremental order 1-bit CTSDM to achieve a large DR, low hardware complexity, and high-energy efficiency. The sensor leverages a hardware sharing strategy to simplify the implementation and reduce power consumption. The proposed CMOS biosensor is integrated within a miniature wireless head mountable prototype for enabling biophotometry with a single implantable fiber in the brain of live mice. The proposed biophotometry sensor is implemented in a 0.18- CMOS technology, consuming from a 1.8- supply voltage, while achieving a peak dynamic range of over a 50- input bandwidth, a sensitivity of 24 mV/nW, and a minimum detectable current of 2.46- at a 20- sampling rate.

A configurable fluorescence sensing front-end for ultra-low power and high sensitivity applications

“…In [2][3][4], CMOS head-mountable optoelectronic neural interfaces for fluorescence sensing are presented. In these works, all the CMOS sensors, light-emitting devices (LED), and optical fiber are enclosed within structures that can be mounted on a mouse's head.…”

“…In these works, all the CMOS sensors, light-emitting devices (LED), and optical fiber are enclosed within structures that can be mounted on a mouse's head. The bio photometry CMOS sensors in [2][3][4] consist of a differential CMOS photodetector with a differential capacitive TIA merged with an incremental 2 nd order continuous-time delta-sigma modulator. The design in [4] provides a high dynamic range with a minimum detectable current of 2.4 pA, although the sensor cannot be fully implantable and wirelessly powered.…”

“…The received emitted light intensity from the cells is proportional to the excitation light intensity of the LED. To avoid photobleaching and phototoxicity of the target cells [4], the fluorescence excitation on the cells is necessary to be a pulse with controlled pulse width, duty cycle, and pulse amplitude. Therefore, there is a need to have a sufficient dynamic range for sensing a wide range of emitted light intensity with different pulse widths.…”

Miniaturized Wireless Cell Spectrophotometer Platform in Visible and Near-IR Range

“…Increasing demand for monitoring and detecting the chemical composition of different materials using optical interfaces emphasizes the importance of the qualitative and quantitative data collected from each of them. Having such information for different materials can help in a vast area of applications [1,2,3], including identifying toxic substances, biopsy, testing foods and water quality, tracking environmental changes, and monitoring health, each of which has many subsets. For example, health monitoring includes the course of treatment, chronic disease management, pathogen detection, and early disease detection.…”

“…Much effort has been devoted to creating miniaturized spectroscopy devices over the past number of years due to the increasing demand for battery-operated portable equipment and power-saving circuits [3,4]. Following these efforts, in this paper, a low-cost, low-power, miniaturized optical platform is developed using discrete, commercial, offthe-shelf components.…”